The present invention relates generally to ignition systems for internal combustion engines and in particular to improvements in ignition systems of the capacitor discharge type as disclosed in the copending application of Richard J. Maier and myself for Ignition System, Ser. No. 395,908 filed Sept. 10, 1973 and assigned to the assignee of this application. The teachings of that application are incorporated herein by reference thereto.
In order to reduce the complexity, the number of component parts, the package size, and the cost of capacitor discharge ignition circuits, various circuit arrangements have been tried in an attempt to improve such circuits without sacrificing desired operating performance and reliability. In accordance with such objectives, the prior art includes various circuit arrangements for charging the capacitor during a portion of the engine operating cycle and thereafter discharging the capacitor, through an SCR or the like, at a desired time in the engine cycle.
The aforementioned application is directed to improvements in capacitor discharge ignition systems, and particularly, to a capacitor discharge ignition system having novel features which result in important advantages over prior art capacitor discharge ignition systems, i.e. a capacitor discharge ignition system which can provide excellent performance over a wide range of engine speeds without the complexity generally associated with prior capacitor discharge ignition systems. One of these features of the invention of the aforementioned application is the elimination of a separate winding for providing a trigger signal for the SCR whereby the cost and complexity of the system are reduced. Another feature of the invention of the aforementioned application is the provision of an ignition coil on the stator structure having the charge/trigger winding so that the primary winding of the ignition coil is energized, not only by the discharge of the capacitor, but also simultaneously by the magnetic field used to induce a charging current in the charge/trigger winding so as to increase the power supplied to the spark plug.
The invention of the present application is an improvement in the invention of the aforementioned application in that it provides an ignition system having substantially the same performance as the ignition system of the aforementioned application and yet desirably may utilize circuit components having lower peak potential ratings thereby still further reducing the cost of the system. It will be appreciated that as the peak potential rating of circuit components such as SCR's increases, the cost of these components dramatically increases. It will further be appreciated that in simple electrodynamic devices such as the rotors and stators for use with low-cost engines, irregular potential waveforms result which may have substantial potential peaks or spikes. Consequently, high potential peaks developed by these electrodynamic devices can result in the need for circuit components with very high peak potential ratings.
In accordance with the present invention, an ignition system is provided in accordance with the teachings of the aforementioned application which additionally has a shorted turn about one leg of the stator structure and/or has a diode connected in parallel with the single charging and triggering coil. These components have been found to substantially decrease the maximum peak potential delivered to the circuit components, for example, by approximately 50%. Importantly, and unexpectedly, the use of these devices does not detrimentally reduce the potential developed at the secondary coil at low rotor speeds such as those occurring during cranking of the engine. Accordingly, this discovery is believed to be a significant advance in this art.